Eval() and Bind() Two-Way DataBinding Expressions in Asp.Net

The ASP.NET Framework supports both one-way DataBinding expressions and two-way DataBinding expressions.

In a oneway DataBinding expression, you use the DataBinding expression to display the value of a data item. You use the Eval() method to display the value of a one-way DataBinding expression.

In a two-way DataBinding expression, you not only can display the value of a data item,
you also can modify the value of a data item. You use the Bind() method when working with a    two-way DataBinding expression.

Example:

Suppose you have a movies table in your database. It has columns named Id, Title, Director, DateReleased.

<asp:FormView id="FormView1" DataKeyNames="Id" DataSourceId="srcMovies" DefaultMode="Edit" AllowPaging="true" Runat="server">
<EditItemTemplate>

<asp:Label
id="lblTitle"
Text="Title:"
AssociatedControlID="txtTitle"
Runat="server" />

<asp:TextBox
id="txtTitle"
Text='<%#Bind(“Title")%>'
Runat="server" />
<br />

<asp:Label
id="lblDirector"
Text="Director:"
AssociatedControlID="txtDirector"
Runat="server" />

<asp:TextBox
id="txtDirector"
Text='<%#Bind(“Director")%>'
Runat="server" />
<br />

<asp:Button
id="btnUpdate"
Text="Update"
CommandName="Update"
Runat="server" />
</EditItemTemplate>
</asp:FormView>

<asp:SqlDataSource id="srcMovies" ConnectionString="yourConnectionString"
SelectCommand="SELECT Id, Title,Director,DateReleased FROM Movies"
UpdateCommand="UPDATE Movies SET Title=@Title,
Director=@Director WHERE Id=@Id"
Runat="server" />

The FormView contains an EditItemTemplate. The EditItemTemplate contains three TextBox controls. Each TextBox control has a two-way DataBinding expression assigned to its Text property.

The DataBinding expressions associate the TextBox control properties with the properties of the data item being edited. When you click the Update button, any changes you make to the Text properties are updated in the Movies database table.